The general objectives of the proposed work are to define some of the interactions between biologically active peptides from blood and specific target cells in the lung, and to determine how these interactions relate to tissue injury and inflammation. There will be particular emphasis upon the actions of peptides on mast cells and endothelial cells. Vasoactive peptides of particular interest include the complement-derived anaphylatoxins, C3a and C5a, and the kinins. An initial approach to the problem was exploration of the biochemical properties of cultured endothelial cells. This included a study of inactivation of vasoactive peptides by cultured cells. Currently, the influence of peptides on endothelium, with respect to the biochemical and morphologic properties, is under investigation. The effect of vasoactive peptides on mast cells and histamine release is also being studied. BIBLIOGRAPHIC REFERENCES: Johnson, A. R. and Erosd, E.G.: Angiotensin I converting enzyme in human endothelial cells. Circulation 52: Suppl. II 59, 1975 (Abst). Erdos, E.G., Johnson, A.R. and Robinson, C.J.G.: Release of angiotensin I converting enzyme from the shocked rat lung. Circulation 52: Suppl. II 88, 1975.